The present invention relates to a differential pressure transmitter and, more particularly, to a differential pressure transmitter which is excellent in detecting a temperature change of a processed fluid.
In a pressure receiving structure of a conventional differential pressure transmitter, as disclosed in Japanese Patent Unexamined Publication No. 60-185130 (see FIG. 2), seal diaphragms for receiving pressures of first and second fluids are connected on opposite sides of a pressure receiving member so as to form first and second pressure receiving chambers, respectively. A center diaphragm for defining first and second damper chambers, a semiconductor sensor and its support member are provided inside of the pressure receiving member. Further, a pressure passage for connecting the first pressure receiving chamber and the first damper chamber, another pressure passage for connecting the first damper chamber and the semiconductor differential-pressure sensor, still another pressure passage for connecting the second pressure receiving chamber and the second damper chamber, and a pressure passage for connecting the second damper chamber and the semiconductor differential-pressure sensor are formed to apply pressures from the first and second pressure receiving chambers to the semiconductor sensor through the first and second damper chambers, respectively. With this structure, even if an excessive pressure is applied, breakage of the semiconductor sensor for detecting the differential pressure is prevented.
Also, in the conventional differential pressure transmitter, a thermistor is provided on the semiconductor sensor so as to prevent an error in differential pressure detection due to a temperature change of a processed fluid. On the basis of a signal output from the thermistor, a differential pressure of the processed fluid produced from the differential pressure sensor is corrected, to thereby produce an accurate differential-pressure signal.
Moreover, in relation to the maintenance of the differential pressure transmitter, in order to inspect the first and second seal diaphragms connected on the opposite sides of the pressure receiving member, bolts which fasten the pressure receiving member and flanges are loosened, and the pressure receiving member is detached from the main body before inspecting the seal diaphragms.
Furthermore, when a differential pressure transmitter is used, it is necessary to perform inspections regularly as to whether the zero point (the condition where the output of the transmitter is 0% when the differential pressure is 0 mmH.sub.2 O) varies or not. In the conventional differential pressure transmitter, a special three-way valve is required to be provided between the differential pressure transmitter and the piping so that the higher-side pressure and the lower-side pressure will be equal, i.e., the differential pressure is 0 mmH.sub.2 O, while the transmitter is kept connected to the piping.